The international community must support Dhaka in its standoff with gangs of violent Islamic radicals.

Nobody can accuse Bangladesh's radical Muslims of mincing their words. On Sunday, a swarm of tens of thousands descended in a fury on Dhaka to demand death for bloggers accused of defaming the prophet Muhammad. "One point, one demand, atheist bloggers must be hanged!" the mobs chanted. Two days of rioting and arson later, at least 22 people lay dead as security forces battled to restore law and order in the nation's capital.

This flare-up is only the most recent skirmish in an ongoing war for the future of...